We love to go to Florida and especially Disney. I don't know if you've visited the water parks at Disney but for teenagers they are a lot of fun. My husband and daughter took a helicopter ride while we were in Orlando and really had fun. There are a lot of putt putt courses and beautiful golf courses. Cirque de Solie (I know I spelled that wrong) has a performance that is only done in Orlando. Orlando has a place called Bethlehem (I haven't been but my friend who has loved it), Sea World and Midieval Times.
If you haven't visited the Kennedy Space Center it's very interesting. I didn't know which beach you were talking about. Ron Jon's surf shop is fun at Cocoa Beach, if that's the one you're going to and the space center is there as well. We stayed at a Hampton Inn property on the beach (but it was low season) that was reasonably priced.
As far as eating, there is a Bubba Gump Shrimp restaurant, Planet Hollywood, Rainforest Cafe, Jimmy Buffet Margaritaville, Hard Rock Cafe, Emeril's etc. These restaurants are either in Downtown Disney or Universal Walk. The shopping/restaurants etc are fun to spend the day in both those areas.
Hope you have a wonderful time. September is nice in Orlando area and still very hot. Once we went the end of September and I couldn't believe how really hot it still was.
Blessings,
L.